Purpose:
To date, limited research has focused on the question of further aqueous humor drainage over the bleb in filtration surgery. Recently, it was reported that lymphatic drainage pathways may play an important role in filtration surgery (Yu et al., Prog Retin Eye Res. 2009). Podoplanin (PDN) is one of the potent markers for lymphatic endothelial cells. In this study, we retrospectively investigated whether encapsulated tissue (ECT) due to glaucoma long tube surgery (ECT-GTS) expresses PDN by comparing ECT due to trabeculectomy (ECT-TLE), a leaking bleb, normal conjunctiva, the Tenon’s capsule, and the sclera.

Results:
Fibroblasts in all normal Tenon’s capsule pieces that were not irrigated by aqueous humor did not express PDN. Fibroblasts in whole-thickness ECT-GTS samples obtained within 23 days post tube ligation release expressed PDN, however, those in the center of ECT-GTS obtained after 30 days post tube ligation release expressed PDN only at the site facing the aqueous humor. Strong expression of PDN in fibroblasts was observed at the anterior parts of all ECT-GTS samples, where abundant PDN-positive vessels were observed. A similar pattern of PDN-positive vessels, but less PDN-positive fibroblasts, were also observed in ECT-TLE samples. Blood vessels that stained positive for CD34 and thrombomodulin were observed at the opposite side of ECT-GTS specimens facing the aqueous humor.

Conclusions:
Tenon’s capsule fibroblasts may express PDN when they are irrigated by aqueous humor. Encapsulated tissue may have lymph-like characteristics as a trabecular meshwork, which functions as a filter for cleaning aqueous humor. Although there may be small differences between ECT-GTS and ECT-TLE, lymph-angiogenesis may be important for the formation of ECT in glaucoma filtration surgery.